Interpretive Summary: Bermudagrass is a problematic weed for sugarcane growers in Louisiana and throughout the world. Research was conducted to evaluate the competitiveness of three sugarcane varieties (CP 70-321, HoCP 85-845, and LCP 85-384) currently grown in Louisiana with bermudagrass over a three year crop cycle at two locations. Bermudagrass was allowed to compete with sugarcane in the fall after planting, during the entire plant-cane crop, during the plant-cane and first-ratoon crops, or during all three crops (plant-cane, first-ratoon, and second-ratoon). At one location bermudagrass growth was less in ‘CP 70-321’ during the plant-cane crop than in ‘HoCP 85-845’, but bermudagrass growth was greatest in ‘CP 70-321’ compared to the other varieties during the second-ratoon crop. ‘CP 70-321’ is quicker to emerge following planting than the other varieties which may explain the reduction in bermudagrass growth during the plant-cane crop, but it is also weaker in it’s ability to ratoon, producing fewer stalks than the other varieties, which may explain the greater bermudagrass growth during the second-stubble crop. Competition from bermudagrass reduced sugarcane height and stalk population compared to weed-free sugarcane. Competition from bermudagrass also reduced gross cane and sugar yields, with the largest reductions occurring during the plant-cane crop where sugar yield losses were as high as 32%. Yield losses during the plant-cane crop were reduced equally when bermudagrass was removed in March following planting as to when it was allowed to remain for the entire season. Yield losses in ratoon crops were less and often insignificant and total sugar yield losses for the three year crop cycle were as high as 15%. This study shows the importance of eliminating bermudagrass from sugarcane fields prior to planting, as the majority of yield losses occurred during the plant-cane establishment period.

Technical Abstract:
Research was conducted with the objectives of determining differences in the competitiveness of three phenotypically different sugarcane cultivars, ‘CP 70-321’, ‘HoCP 85-845’, and ‘LCP 85-384’, with bermudagrass, and the effects of bermudagrass interference on sugarcane. Sugarcane was planted at two locations having a history of dense bermudagrass infestations with data being collected in the plant-cane, first-ratoon, and second-ratoon crops. Duration of bermudagrass interference treatments were established by allowing bermudagrass to remain for one, two, or all three years of the crop cycle and were compared with sugarcane kept bermudagrass free for the entire crop cycle and with bermudagrass interfering only in the fall following planting. At one location, bermudagrass biomass was less in CP 70-321 than in HoCP 85-845 in the plant-cane crop, but biomass was greater in CP 70-321 than in the other two cultivars during the second-ratoon crop. CP 70-321 emerges quickly following planting which may have reduced bermudagrass growth in the plant-cane crop, but has lower stalk populations which may have allowed increased bermudagrass survival and growth during the second-ratoon crop. Bermudagrass interference reduced sugarcane stalk populations and heights in all three crops averaged across cultivar. Bermudagrass interference reduced gross sugarcane and sugar yields by as much as 28% and 32%, respectively, in the plant-cane crop, with lesser reductions in the first- and second-ratoon crops. Total gross sugarcane and sugar yields for the three crops were reduced by as much as 13 and 15%, respectively. Yield reductions over the three-year crop cycle can primarily be attributed to losses that occurred in the plant-cane crop showing the importance of controlling bermudagrass prior to planting and during establishment of the plant-cane crop.